At The Motley Fool, we understand that it often pays to zig when Wall Street zags, but that doesn't mean that we don't pay attention to what leading fund managers are buying and selling. And funds that aren't always in lockstep with the broader market can be a particularly valuable source of insight.

Every quarter, fund managers overseeing more than $100 million must disclose their quarter-end holdings publicly by filing Securities and Exchange Commission Form 13-F. The form lists all U.S.-traded securities the manager held at the end of the quarter. Although the form doesn't disclose the manager's short positions or the manager's intraquarter trades, it can shine a bright light on his or her "long" stock bets.

Q3 2011 update
George Soros is known to some folks these days for his politics and philanthropy, but his fame stems from his wealth, which is a result of his outstanding investing prowess. He founded Soros Fund Management back in 1973, and under its umbrella, the Quantum Fund racked up an amazing record, reportedly averaging close to 20% annual growth over four decades.

As The New York Times has explained, "His huge gains have come from macro bets, which aim to profit from global economic trends by trading currencies, commodities, bonds and other securities. Mr. Soros made his name, however, betting on currencies."

The total market value of Soros Fund Management's disclosed equity holdings as of Sept. 30, 2011 -- the latest quarter for which data is available -- was $5.8 billion. Its 10 largest positions and associated changes in number of shares held as of Sept. 30, 2011 were:    

   Motorola Solutions (NYSE: MSI) -- increased 16.5%.
    Adecoagro (NYSE: AGRO) -- reduced 3.6%.
    Interoil (NYSE: IOC) -- increased 10.7%.
    Emdeon (NYSE: EM) -- reduced 26.1%.
    Westport Innovations (Nasdaq: WPRT) -- reduced 37%.
    Visteon (NYSE: VC) -- increased 2.6%.
    Amazon.com (Nasdaq: AMZN) -- increased 1,516%.
    Exar (Nasdaq: EXAR) -- unchanged.
    DISH Network (Nasdaq: DISH) -- reduced 1.5%.
    Apple (Nasdaq: AAPL) -- increased 17.8%.

During the quarter, Soros Fund Management also increased its position in Kraft Foods, Heartware International, and YPF, among others. Among the stocks that it reduced its exposure to were Dendreon (Nasdaq: DNDN) and Seagate Technology. Also, it sold out of some stocks entirely, such as RF Micro Devices (Nasdaq: RFMD) and Petroleo Brasiliero.

Dendreon generated a lot of excitement when its anti-prostate-cancer drug, Provenge, was approved, but many doctors are not prescribing it, perhaps due to its steep $93,000 cost. Radio frequency technology specialist RF Micro Devices, meanwhile, is reporting strong sales in China and is growing its market share in telecommunications. Soros' company may have lost faith in it due to its close ties to struggling Nokia.

Here's where Soros Fund Management has been winning and losing and making new bets:

Recent winner
Westport Innovations was a big winner in the third quarter, rising 20% when the S&P 500 sank by about 14%. Bulls are excited by its position in the burgeoning natural-gas-fueled vehicle market. The company has a five-star (out of five stars) rating at Motley Fool CAPS.

Recent loser
DISH Network didn't do so well, dropping more than 18%. Its detractors aren't excited about its purchase of the bankrupt Blockbuster company and its shrinking customer base. The company has a four-star rating in Motley Fool CAPS.

New bets
The largest new addition is Medicines (Nasdaq: MDCO), a global pharmaceutical concern. Its shares popped recently on news of a settlement with Teva Pharmaceuticals, and my colleague Rich Smith has deemed it an interesting, though speculative, stock. Its anticoagulant medicine has been successful and it has other formulations in its pipeline. The company has a four-star rating at Motley Fool CAPS.

SanDisk (Nasdaq: SNDK) is another new addition. It has struggled some in our shaky economy, but it remains a solid player in flash memory and the more-profitable solid-state drive business. The company has a four-star rating at Motley Fool CAPS.

We should never blindly copy any investor's moves, no matter how talented the investor. But it can be useful to keep an eye on what smart folks are doing. Remember, 13-F forms can be great places to find intriguing candidates for our portfolios.

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